Electric circuit interrupter of the vacuum type with arc-voltage control means for promoting arc transfer



March 5, 1968 J. w. PORTER 3,372,258

ELECTRIC CIRCUIT INTERRUPTER OF THE VACUUM TYPE WITH ARC'VOLTAGE CONTROLMEANS FOR PROMOTING ARC TRANSFER Filed May 28, 1965 2 Sheets-Sheet 1INVENTOR. JOSEPH W PORTER,

ATTORNEY ELECTRIC CIRCUIT INT ERRUPTER OF THE VACUUM TYPE WITHARC-VOLTAGE CONTROL MEANS FOR PROMOTING ARC TRANSFER March 5, 1968 J w,PORTER v 3,372,258

Filed May 28, 1965 2 Sheets-Sheet 2 WW I //v VENTOR. JOSEPH W PORTERUnited States Patent ELECTRIC CIRCUIT INTERRUPTER OF THE VACUUM TYPEWITH ARC-VQLTAGE CON- TROL MEANS FOR PROMOTING ARC TRANS- FER Joseph W.Porter, Media, Pa., assignor to General Electric Company, a corporationof New York Filed May 28, 1965, Ser. No. 459,656 11 Claims. (Cl. 200144)ABSTRACT 0F THE DISCLQSURE A vacuum type circuit interrupter in whicharc transfer to a preferred arcing region of the interrupter is promotedby forcing high cur-rent arcs located outside the preferred arcingregion tob urn with a higher are voltage than when in said preferredarcing region. The lower arc voltage in the preferred arcing region isobtained by a strong magnetic field that is oriented generally parallelto the are when in the preferred arcing region but trans verse to arewhen outside the preferred arcing region.

This invention relates to an electric circuit interrupter of the vacuumtype and, more particularly, to a vacuum type circuit interrupter withnew and improved means for transferring an are from' an arc-initiationregion to a preferred arcing region where the arc voltage developed bythe arc is relatively low.

In application S.N. 328,656Lee, filed Dec. 6, 1963, and assigned to theassignee of the present invention, it is pointed out that the arcvoltage developed by an arc during high instantaneous currents can beappreciably reduced by applying to the are an intense magnetic fieldthat has its lines of force extending axially of the arc. The aforesaidLee application is now abandoned but was replaced by acontinuation-in-part application that issued as Patent 3,321,599.

An object of the present invention is to utilize this low arc-voltagecharacteristic of the vacuum arc in an axial magnetic field to producerapid transfer of the are from an arc-initiation region into a preferredarcing region of the vacuum interrupter.

Another object is to promote arc transfer to a preferred arcing regionof an interrupter by forcing high current arcs located outside thepreferred arcing region to burn with a higher are voltage than when insaid preferred arcing region.

Another object is to provide magnetic means which can increase thedifference between the arc voltage developed when the arc is in thepreferred arcing region and that developed when the arc is outside thepreferred arcing region.

Still another object is to utilize the tendency of an arc to move into aposition of minimum arc voltage for promoting division of the are into aplurality of series-related arcs.

In carrying out my invention in one form, I provide, within a highlyevacuated envelope, a first electrode and a second electrode. The secondelectrode has a position during interruption spaced from the firstelectrode to define a primary arcing gap therebetween across which anarc is established. Means is provided for developing a magnetic fieldthat has its lines of force extending transversely of an arc in saidprimary gap. Means including an auxiliary electrode electricallyconnected to the first electrode is provided to define a secondaryarcing gap into which the arc is movable from said primary arcing gap.This secondary arcing gap is so disposed that the lines of force of saidmagnetic field in the region of any are in the secondary arcing gapextend generally parallel to this are. The magnetic field is controlledin such a manner that its flux density in the region of an arc in thesecondary gap during instantaneous currents greater than 20,000 ampereswill be high enough to substantially reduce the arc voltage as comparedto the are voltage normally developed by an are burning across saidsecondary gap without said magnetic field. Means is also provided forsubstantially eliminating said magnetic field across the secondaryarcing gap during the period just prior to current zero following aninstantaneous current greater than 20,000 amperes.

In a preferred form of the invention, the magnetic field has a highenough flux density extending transversely of an arc in the primary gapto increase the arc voltage during high instantaneous currents to alevel substantially higher than the arc voltage normally developed by anare burning across the primary gap without said magnetic field. Thishigher are voltage in the primary gap will increase the differencebetween the arc voltage developed by an arc in the primary gap and thatdeveloped by an arc in the secondary gap, thus accelerating transfer ofthe are from the primary to the secondary gap.

For a better understanding of the invention, reference may be had to thefollowing description taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a sectional view through an interrupter embodying one form ofthe present invention.

FIG. 1a is a sectional view taken along the line 1a1a of FIG. 1.

FIG. 2 is a side elevational view of a portion of FIG. 1.

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1.

FIG. 4 is a sectional view of an interrupter embodying a modified formof the invention.

FIG. 5 is an enlarged view of a portion of the interrupter of FIG. 4.

FIG. 6 is a sectional view of FIG. 4.

FIG. 7 is an enlarged fragmentary view of a portion of a modifiedinterrupter.

FIG. 8 is an enlarged fragmentary view of another portion of theinterrupter of FIG. 7.

Referring now to the interrupter of FIG. 1, there is shown ahighly-evacuated envelope 10 comprising a tubular casing 11 of suitableinsulating material and end structure 12 and 13 closing off the ends ofthe casing 11. Suitable seals 14 are provided between the end structuresand the casing 11 to render the envelope vacuum-tight. The normalpressure within the envelope is lower than 10' mm. of mercury, so that areasonable assurance is had that the mean free path for electrons willbe longer than the potential breakdown paths in the envelope.

The upper end structure 12 comprises an end plate 15 having a centrallylocated opening 16 therein. Mounted atop this end plate is an invertedcup shaped part 17 having a bore 19 aligned with opening 16 in the endplate 15. The cup shaped part 17 is preferably made of ahighresistivity, low-permeability metal such as stainless steel. Thelower surface of the cup shaped part is suitably brazed about its entirecircumference to the end plate 15.

Mounted Within the cup-shaped part 17 is a pair of relatively movablecontacts or electrodes 21 and 22. The upper electrode 21 is a stationaryelectrode that is mounted on a rod 24 of highly conductive material. Thestationary electrode 21 is suitably brazed to the lower end of the rod24. The upper end of the rod 24 extends through the upper end wall ofthe cup-shaped member 17 and is joined thereto by a brazed joint 25 thatforms a vacuumtight seal between the rod and the end wall.

The lower electrode 22 is a movable electrode that is suitably joined toan operating rod 26 of highly conductive material. This operating rod 26freely extends taken along the line 6-6 in a vertical direction througha central opening in the lower end cap 13. The operating rod 26 isvertically movable and can be driven in an upward direction from itsposition of FIG. 1 to move the lower electrode 22 into engagement withthe upper electrode 21, thereby closing the interrupter. Opening of theinterrupter is produced by driving the operating rod 26 downwardly,thereby driving the lower electrode 22 out of engagement with the upperelectrode and into its positon of FIG. 1.

For permitting vertical motion of the operating rod 26 without impairingthe vacuum inside envelope 10, a flexible metal bellows 29 is providedabout the operating rod 26. This bellows 29 is joined at its respectiveopposite ends to the end pate 13 and the operating rod 26 by suitablevacuum-tight joints. For protecting the bellows 29 from arcing productsgenerating during operation of the interrupter, a shield 29a of invertedcup-form is provided about the bellows. This shield is suitably attachedto the operating rod 26.

Each of the illustrated electrodes 21 and 22 is of a disk shape and hasan annular portion 23 near its outer periphery projecting toward theother electrode. These annular portions are in substantial alignmentwith each other and are adapted to engage each other when theinterrupter is in its closed position. Opening of the interrupterinitiates an are 28 across a primary gap 27 between the projectingportions 23, and this are is subsequently extinguished to interrupt thecircuit in a manner that will soon be explained.

Surrounding the lower electrode 22 is a ring-shaped electrode 30. Thisring-shaped electrode 30 is mounted on the cup-shaped housing 17 and iselectrically connected to the upper electrode structure 21, 24 through aconnecting strap 32 of high conductivity material. The connecting strap32 is suitably brazed at its upper end to the rod 24 and at its lowerend to the ring shaped electrode 30. Suitable spacers 31, preferably ofstainless steel, are suitably brazed between the housing 17 and theelectrode 30 and strap 32 to support these parts on the housing 17 inspaced relationship thereto. There is an annular space 34 between thering-shaped electrode 30 and the lower electrode 22 that serves as anarcing gap of annular form to which the arc is transferred after beinginitiated between the relatively movable electrodes 21 and 22.

In order to reduce the arc voltage developed by a high current areextending radially across the annular gap 34, I provide field-producingmeans 40 for developing an intense magnetic field that has its lines offorce extending in a radial direction across the annular gap 34.Referring to FIG. 3, since an are, such as 28a, across this annular gap34 will also extend radially thereof, the lines of force of the magneticfield in the region of an are positioned in the gap 34 will extendgenerally parallel to the axis of the arc. As explained in theaforementioned Lee application S.N. 328,656, such a parallel magneticfield will reduce the arc voltage developed by such an arc during highinstantaneous currents, e.g. above 20,000 amperes. In a preferred formof the invention, the magnetic field strength is made high enough toreduce the arc voltage developed during peak currents greater than40,000 amperes to less than half the arc voltage normally developed byan arc of corresponding peak current with no axial magnetic fieldpresent.

The field-producing means 40 comprises a pair of seriesconnected coils42 and 44 wound about the cup-shaped housing 17. These series-connectedcoils 42 and 44 are connected in series with the electrodes 21 and 22 ofthe interrupter between a terminal 43 of the interrupter and theconductive rod 24. As illustrated in FIG. 2, these coils 42 and 44 arewound in opposite directions so that the magnetic field produced by thetwo coils buck or oppose each other. The field produced by each coil isreferred to hereinafter as a sub-field. The sub-field produced by coil42 is shown at 45, and the sub-field produced by coil 44 is shown at 46.The lines of force of each of these sub-fields surround the particularcoil producing the field and extend radially of each coil in the regionbetween the two coils. These sub-fields may be thought of as being of agenerally toroidal shape. They surround the longitudinal axis of theelectrodes 21 and 22 and are axially displaced from each other alongthis axis. Since both the sub-fields traverse the region between the twocoils, a relatively high field strength is developed in this particularregion. It will be apparent from FIGS. 1 and 3 that the magnetic fieldin this region extends radially of the annular gap 34 between theconcentric electrodes 30 and 22 around the entire circumference of thegap 34. It will also be apparent from FIG. 1 that the magnetic fieldextends radially of the arc-initiating gap 27 between the two electrodeportions 23.

Since the coils 42 and 44 are in series with the electrodes 21 and 22,it will be apparent that the above-described magnetic field has a highflux density or intensity when the current through the interrupter ishigh and a low flux density or intensity when the current through theinterrupter is low. This is as desired since the high intensity of themagnetic field is used for reducing the arc voltage during highinstantaneous currents, whereas the low intensity during low currentsallows the interrupter to recover its dielectric strength at currentzero without substantial interference from the magnetic field.

As pointed out hereinabove, downward opening movement of electrode 22initiates an are 28 across the arcinitiating gap 27. Thepreviously-described magnetic field 45, 46 will extend transversely ofthis arc. I have found that an intense magnetic field directedtransversely of a high current vacuum arc will cause it to burn at ahigher are voltage than it would in the absence of the transverse field.It has also been found that there is a strong tendency on the part of anarc to move into a position where it can burn with minimum arc voltage.I capitalize on this tendency by providing, immediately adjacent the gap27, the annular gap 34 where the am can extend axially of the magneticfield 45, 46 and can thus burn at a very low arc voltage, as previouslydescribed. FIG. 3 shows the are at 28a extending radially across theannular gap 34. The immediate proximity of this annular gap 34 where thearc can burn with a low arc voltage results in the are moving rapidlyfrom the high arc-voltage gap 27 into the low arcvoltage gap 34.

The are continues to burn in the gap 34 until a natural current zero isreached, at which time the gap quickly recovers its dielectric strengthand prevents reignition of the arc.

The presence of a strong axial magnetic field between the electrodes atcurrent zero would have a tendency to impair the gaps ability to recoverits dielectric strength. My interrupter contains a number of featureswhich prevent such impairment of the gaps ability to recover itsdielectric strength. One is that the current-responsive fieldproducingmeans 42, 44 is connected in series with the arc. Thus, when the arcingcurrent approaches zero, the current through the field-producing meansapproaches zero, and the field strength likewise approaches zero. Eddycurrents induced in adjacent parts of the interrupter tend to produce alag between flux and current which maintains flux in the gap at currentzero. But I reduced this lag to a tolerable value by severely limitingthe eddy currents.

For the purpose of suppressing such eddy currents, 1 form the cup-shapedmember 1'7 of stainless steel, a highresistivity, low-permeabilitymetal, in which negligible eddy currents are induced. I also provide aslot 50 (best shown in FIG. 1a) in the ring-shaped electrode 30 whichsubstantially prevents eddy currents from finding a path extendingcircumferentially about the ring-shaped electrode 30. The mainelectrodes 21 and 22 are also provided with radially extending slots 52that break up the eddy current paths through the electrodes. These slots52, which are best shown in FIG. 3, are extended radially inward as faras possible so as to improve their effectiveness in breaking up the eddycurrent paths. Also each electrode is perforated in its central region,as shown at 55, to further reduce the eddy currents.

The slots 52 serve the additional function of producing movement of thearc in a circumferential direction about the periphery of lowerelectrode 22. In this connection, the slots 52 force the net currentflowing through the electrode 22 to an arc terminal on the peripheralportion of the electrode 22 to follow a path that has atangentiallyextending component. For example, note the radiallyextending arc 28a of FIG. 3 and the current path L extending through theelectrode 22 generally tangentially with respect to the arc. Asexplained in US. Patent 2,949,520- Schneider, assigned to the assigneeof the present invention, the magnetic effect of current flowing throughsuch a tangentially extending path is to drive the arccircumferentially.

Additional force for driving an are such as 28a in a circumferentialdirection results from the presence of slot 50 in the ring-shapedelectrode 30. This slot 58 forces current flowing through the elect-rode30 .to an arc terminal at substantially any point on the ring-shapedelectrode 30 to follow a portion of path L that extendscircumferentially with respect to the ring electrode. The magneticeffect of current flowing through such a path is to lengthen the loop inthe path L by driving the arc circumferentially. By driving the arccircumferentia-lly while maintaining its arc voltage low, I can limitthe quantity of arcing products generated during interruption, therebyimproving the ability of the interrupter to recover its dielectricstrength at current zero.

For protecting insulating casing 11 from the deposition of arc-generatedelectrode vapors thereon, a suitable metal shield 57 of tubular form isprovided. This shield is shown connected to end plate 15. An auxiliaryshield 58 surrounds the lower end of shield 57 to provide additionalprotection against vapor-deposition for the tubular insulating casing11.

FIG. 4 illustrates a modified form of the invention where the initialarc is first divided into two series-related arcs, and each of theseseries-related arcs is subsequently transferred to a region of low arcvoltage, where there is an intense magnetic field extending axially ofthe are This interrupter of FIG. 4 comprises a highly-evacuated envelopecomprising a tubular insulating casing 11 and end plates 12 and 13suitably sealed to the casing 11 at its opposite ends. Mounted Withinthe sealed envelope 10 is a pair of relatively movable contacts, orelectrodes, 78 and 72. These contacts are of a generally cup-shape, eachcomprising a base portion 73 and cylindrical flange 74 projecting awayfrom the base portion 73 in a direction away from the other contact. Theupper contact 74) is a stationary contact, and the lower contact 72 is amovable contact that can be moved in a vertical direction into and outof engagement with the upper contact.

The movable lower contact 72 is mounted on a conductor 77 of a highconductivity material, such as copper, that is spirally wound into acoil 78 of generally cylindrical form. This conductor 77 is suitablyjoined at its upper end to the base of the movable contact 72 and at itslower end to an operating rod 80 of high conductivity material thatprojects freely through the lower end cap 13. Suitable spacers 82 of ahigh resistivity material such as stainless steel are located betweenthe turns of the coil to maintain a definite spacing therebetween. Thesespacers 82 are preferably held in position by suitable brazed joints.The spacers also structurally reinforce the coil and impart rigiditythereto. Since stainless steel has a very high resistivity in comparisonto that of the copper used for conductor 77, very little of the currentflows through the spacers. Nearly all the current is forced to followthe spiral path followed by the conductor '77.

The upper contact 70 is mounted on a coil 78a of substantially the sameconstruction as the lower coil 78. Thus, the upper coil is formed from aconductor 77a that ex tends in a spiral path and has stainless steelspacers 82a maintaining a slight spacing between adjacent turns. Forreasons which will soon appear more clearly, the upper coil is wound inan opposite direction from the lower coil. The upper coil 78:: issuitably joined at its upper end to a copper conductor 83 that extendsthrough the upper end cap 12. A suitable brazed joint 84 is providedabout the upper conductor 83 to mechanically support it and provide avacuumtype connection between the conductor 83 and the end cap 12.

The operating rod 86 is mounted for vertical reciprocation. It can bedriven in an upward direction to carry the movable contact '72 intoengagement with the stationary contact 70, thereby closing theinterrupter. The operating rod 88 can be driven in a downward directionto separate the movable contact '72 from the stationary contact 70,thereby opening the interrupter, as will soon be described. A flexiblemetallic bellows 29 provides a seal between the end cap 13 and operatingrod 80 and thus permits vertical movement of the rod 80 withoutimpairing the vacuum inside the envelope l0. Suitable operating means(not shown) is provided for effecting upward closing and downwardopening movement of the rod 80.

Each of the contacts 7% and 72 has an annular portion 73a near its outerperiphery projecting toward the other contact. These annular portionsare in substantial alignment and are adapted to engage each other whenthe interrupter is in its closed position. Opening of the interrupterinitiates an arc such as shown at 85 between the projecting portions73a. This are is referred to herein after as the primary arc, and thegap between projecting portions 73a is referred to as primary gap 86.

Surrounding the primary gap 86 is a tubular arcdividing electrode 88 ofa high conductivity material such as copper. This tubular arc-dividingelectrode 88 is supported on casing 11 by pins 89 extending radiallythrough the casing 11 in sealed relationship thereto. Under normalconditions, this arc-dividing electrode 88 is electrically isolated fromboth of the contacts 70 and 72.

At opposite ends of the arc-dividing electrode 88 are secondaryelectrodes 90 and 92 eiectrically connected to the contacts 7t? and 72,respectively. The upper secondary electrode 90 is an annular disk thatis an extension of flange 74 of the cup-shaped contact 79 and extendsgenerally perpendicular to the flange 74. The lower secondary electrode92 is an annular disk that is an extension of flange 74 of cup-shapedelectrode 72 that extends generally perpendicular to the flange. Theannular space between the upper secondary electrode and the upper end ofthe arc-dividing electrode 88 is referred to as a secondary arcing gap95, and the annular space between the lower secondary electrode 92 andthe lower end of electrode 88 is referred to as a secondary arcing gap96.

The primary are 85 that is initiated across the primary arcing gap 86 isdivided by the arc-dividing electrode 88 into two series-related arcswhich are respectively driven into the secondary arcing gaps 95 and 96.More specifically, the primary are 85 is initiated in a positionradially spaced from the central axis of the interrupter. Accordingly,current flowing through the arc in the contacts '70 and '72 follows aloop-shaped path L that has a magnetic effect tending to lengthen theloop and drive the arc in a radially outward direction. In movingradially outward, the are 85 engages the arc-dividing electrode 88. Thisresults in two ser'es-related arcs being formed in approximately theposition and 102. The upper arc at 100 is quickly driven in an upwarddirection through position 103 and thence into a position 105 across thesecondary gap 95. The lower are at 102 is quickly driven in a downwarddirection through position 107 and then into a position 199 across thesecondary arcing gap 96.

In carrying out my invention in this embodiment, I utilize the magneticfield from coils 78 and 78a to accelerate the above-describedarc-dividing action and the subsequent transfer of the series-relatedarcs to the secondary arcing gaps 95 and 96. This can best be understoodby referring to FIG. which illustrates the magnetic field that isdeveloped by the two coils. This magnetic field may be throught of asconstituting two sub-fields 110 and 112, each of a generally toroidalshape. The lines of force of each toroidal shape sub-field are shown at115 following loop-shaped paths surrounding and linked with theirrespective field-producing coils. The two toroidal subfields 110 and 112surround the central longitudinal axis of the interrupter and areaxially displaced from each other along this axis. The centrallongitudinal axis substantially coincides with the axes of coils 78 and78a. Since the coils 78 and 78a are wound in opposite directions, andcurrent flows in series through them, the subfields 110 and 112 are inbucking or opposing relationship to each other. In view of this opposingrelationship, the sub-fields, at any given instant, extend in oppositedirections to each other along the central axis of the interrupter butextend in generally the same radial direction in the region where thetwo sub-fields are adjacent each other.

It will therefore be apparent that the two sub-fields 110 and 112 extendradially of the primary gap 86 and radially of the primary arc 85established thereacross. It will be further apparent that the magneticfield extends perpendicular to the series-related arcs in positions 199,103, 102 and 197. It is only when the series-related arcs reach theimmediate region of the secondary gaps 95, 96 that they enter a positionWhere the magnetic field is generally parallel to the arc.

The magnetic field strength in the secondary arcing gaps 95 and 96 is'made high enough to produce a substantial reduction, preferably 50percent or more, in the arc voltage at which each of these arcs willburn thereacross as compared to the arc voltage that would normally bedeveloped by an arc of the same current but without the strong axialmagnetic field. Since there is no position other than the secondaryarcing gaps 95 and 96 where the are or arcs can extend parallel to thestrong magnetic field, they burn at a higher voltage in locationsoutside the secondary gaps 95 and 96. Since an arc has a strong tendencyto move into a position where it can burn with minimum arc voltage, theprimary are 85 moves rapidly toward the secondary gaps. Such motionforces the primary arc to divide into the above-described series-relatedarcs, which in turn move rapidly into positions of minimum arc voltageacross the gaps 95 and 96.

To further accelerate the transfer of arcing from the primary gap 86 tothe secondary gaps 95 and 96, I make the field strength of the magneticfield in regions outside the secondary arcing gaps so high that the arcvoltage developed is even higher than that which would normally bedeveloped without a strong radial field. This higher-than-normal arcvoltage increases the difference between the arc voltage that the arcwill develop outside the secondary gap 95 or 96 as compared to insideand, thus, further encourages the arc to transfer to the secondaryarcing gap 95 or 96, where the arc voltage will be low.

Since the coils 78 and 79a are in series with any are between theelectrodes, it will be apparent that the magnetic field extendingaxially of the series-connected arcs falls to a low value at and justbefore current zero. For suppressing eddy currents in order to reducethe lag between flux and current to a tolerable value, therebyminimizing the field strength of any residual magnetic field remainingat current zero, I suitably slot all the high conductivity parts of theinterrupter in the arcing region.

For example, referring to FIG. 6, the arc-dividing electrode 88 is shownwith a longitudinally extending slot 129, and the electrode 72 is shownwith a pair of longitudinally-extending slots 122. The other electrode70 has a similar pair of longitudinally-extending slots (not shown).These longitudinally-extending slots in parts 83, 7t) and 72 break upcircumferentially-extending paths for any 8 eddy currents induced inthese parts by the magnetic field. Holes 124 in the base 73 of thecontacts further break up eddy current paths.

By substantially eliminating the axial magnetic field at and just priorto current Zero, I prevent any substantial impairment of the dielectricstrength of gaps and 96 by the axial field.

For condensing the arc-generated vapors that are projected radiallyoutward from the gaps 95 and 96 during interruption, suitablevapor-condensing shields 139 and 132; of tubular form surrounding thesegaps are provided. These shields are preferably formed of ahigh-resistivity, low-permeability material such as stainless steel,which allows negligible eddy currents to be induced therein. If it isdesired to use a high conductivity material for the shields, theinduction of eddy currents therein can be suppressed by constructing theshields as shown in application Ser. No. 454,282-Porter and Polinko, nowPatent No. 3,345,484 filed May 10, 1965, and assigned to the assignee ofthe present invention. The upper shield is electrically isolated fromthe arc-dividing electrode 88 and the upper contact 70 and is preferablyat a midpotential with respect to these parts when the circuitinterrupter is open. The lower shield 132 is electrically isolated fromthe arc-dividing electrode 88 and lower contact 72 and is preferably ata mid-potential with respect to these parts when the interrupter isopen.

For intercepting any arc-generated vapors that might bypass the shields139 and 132, suitable end shields 134 of tubular form are also provided.In addition, a tubular central shield 135 surrounding the adjacent endsof shields 13d and 132 is provided.

The radial magnetic field in which the arcs are located until they reachthe secondary gaps 95 and 96 serves not only to develop a high arevoltage which accelerates arc transfer to the secondary gaps, but italso acts to rotate the arcs about the central axis of the interrupter.In this regard, the radially-extending magnetic field extendstransversely of the arc and coacts with the magnetic field produced bycurrent flowing through the arc to develop a magnetic pressure at oneside of the arc which drives the are normal to the magnetic field. Thisare motion normal to the direction of the magnetic field carries the arcin a circumferential direction about the central axis of theinterrupter. This circumferential arc motion is advantageous in reducingthe quantity of electrode material vaporized by the arc, thusfacilitating circuit interruption at a current zero.

In a modified form of the invention, I continue to rotate theseries-related arcs about the central longitudinal axis of theinterrupter when they are located in the secondary gaps 95 and 96. Theforce for effecting such arc-rotation is derived from a series ofangularly-spaced skewed slots 139 provided in the tubular electrode 88at its free ends. These slots are best illustrated in FIG. 7, where theyare shown angularly overlapping their adjacent slot and dividing the endof tubular part 88 into a series of angularly-spaced fingers 149respectively located between adjacent slots. Each of the slots 139 has acircumferentially-extending component that forces the current flowing toor from an arc terminal located on any one of the fingers 140 to followa path that has a net component extending circumferentially 0f thetubular part. The magnetic effect of current flowing in such acircumferentially-extending path is to drive the arcletcircumferentially of the tubular part about the longitudinal axis of theinterrupter.

Additional force for rotating the arcs in secondary gaps 95 and 96 canbe developed by providing the flanges 9i) and 92 with slots 142, eachextending from the radially outer edge of the flange inwardly via a pathhaving a circumferentially-extending component. Such slots 142 are shownin FIG. 8 defining fingers 143 therebetween in the flange 92. Theseslots force the current flowing through a finger 143 to an arc terminalon the finger to have a circumferenlially-extending component that actsto drive the arc circumferentially.

Another desirable feature of the interrupter of FIG. 4 is that theprimary gap 86 is remote from the secondary gaps 95 and 96 and is wellprotected by the tubular parts 88 and 74 from being contaminated witharc-generated vapors from the secondary gaps. These vapors tend tocondense on the tubular parts before they can reach the primary gap 86.Protecting the primary gap from such contamination helps it to rapidlydevelop a high dielectric strength at current zero.

To inhibit the vapors generated at either of the secondary gaps 95 and96 from reaching the other secondary gap, the arc-dividing electrode 88is preferably provided with an annular portion 145 projecting radiallyinwardly thereof in its central region. The presence of thisradiallyinward projecting portion 145 also facilitates division of theare 85 into its series-related parts, as described hereinabove.

While'I have shown and described particular embodiments of my invention,it will be obvious to those skilled in the art that various changes andmodifications may be made without departing from my invention in itsbroader aspects, and I, therefore, intend in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An alternating current electric circuit interrupter of the vacuumtype comprising:

(a) a first electrode,

(b) a second electrode having a position during interruptions spacedfrom said first electrode to define a primary arcing gap therebetweenacross which an arc is established,

(c) an evacuated envelope surrounding said electrodes,

((1) means for developing a magnetic field that has its lines of forceextending transversely of an arc in said primary gap,

'(e) means including an auxiliary electrode electrically connectedtosaid first electrode for defining, a secondary arcing gap into whichsaid are is movable from said primary arcing gap,

(f) said secondary gap being so disposed that the lines of force of saidmagnetic field in the region of any are in said secondary arcing gapextend generally parallel to said arc,

(g) means for controlling said magnetic field in such a manner that itsflux density in the region of an arc in said secondary gap duringinstantaneous currents greater than 20,000 amperes will be high enoughto substantially reduce the arc voltage as compared to the arc voltagenormally developed by an arc of equal current burning across saidsecondary gap without said magnetic field,

(h) and means for substantially eliminating said magnetic field acrosssaid secondary gap during the period just prior to current zerofollowing an instantaneous arcing current greater than 20,000 amperes.

2. The interrupter of claim 1 in combination with means for maintainingsaid magnetic field transverse to said are from the point at which theare is established between said electrodes to the point at which itreaches the region of said secondary gap.

3. The interrupter of claim 1 in combination with means for rotatingsaid are about a predetermined axis of said electrodes during movementbetween said primary gap and said secondary gap.

4. The interrupter of claim 1 in combination with means for rotatingsaid arc about a pretedermined axis of said interrupter when said are isin said secondary gap.

5. The interrupter of claim 1 in which said magnetic field has a highenough flux density extending transversely of an arc in said primary gapto increase the are 10 voltage during high instantaneous currents to alevel substantially higher than the arc voltage normally developed by anarc of corresponding current burning across said primary gap withoutsaid magnetic field.

6. An alternating current electric circuit interrupter of the vacuumtype comprising:

(a) a first electrode,

(b) a second electrode having a position during interruptions spacedfrom said first electrode to define a primary arcing gap therebetweenacross which a primary are is established,

(c) an evacuated envelope surrounding said electrodes,

(d) means for developing a magnetic field that has its lines of forceextending transversely of an arc in said primary gap,

(e) means for dividing said primary arc into a plurality ofseries-related arcs in an arc-dividing region,

(f) means defining a plurality of secondary arcing gaps for respectivelyreceiving said series-related arcs,

(g) said secondary gaps being so disposed that the lines of force ofsaid magnetic field in the region of any arc in said secondary arcinggaps extend generally parallel to said are in said secondary arcinggaps,

(h) means for controlling said magnetic field in such a manner that itsflux density in the region of an arc in a secondary gap duringinstantaneous currents greater than 20,000 amperes will be high enoughto substantially reduce the arc voltage as compared to the arc voltagenormally developed by an arc of corresponding current burning acrosssaid secondary arcing gap without said magnetic field,

(i) and means for substantially eliminating said magnetic field acrosssaid secondary gaps during the period just prior to current zerofollowing an instantaneous arcing current greater than 20,000 amperes.

7. The interrupter of claim 6 in which said magnetic field extendstransversely of said primary arc and said series-connected arcs in saidarc-dividing region.

8. The interrupter of claim 6 in which said magnetic field extendstransversely of said primary arc and said series-connected arcs in saidarc-dividing region and in which means is provided for maintaining saidmagnetic field transverse to each of said series-related arcs at allpoints in the travel of said series-related arcs between saidarc-dividing region and the region of said secondary gaps.

9. The interrupter of claim 6 in which said magnetic field comprises twosub-fields each of generally toroidal shape, the two generally toroidalsub-fields surrounding a common axis and being displaced from each otheralong said axis,

(a) first field-producing means for producing and shaping one of saidsub-fields in such a manner that its lines of force follow loop-shapedpaths extending through said primary gap radially thereof and throughone of said secondary gaps in a direction generally normal to the radialdirection through said primary ('b) second field-producing means forproducing and shaping the other of said sub-fields in such a manner thatits lines of force follow loop shaped paths extending through saidprimary gap radially thereof and through the other of said secondarygaps in a direction generally normal to the radial direction throughsaid primary gap,

(c) said two sub-fields being developed in bucking relationship to eachother so as to extend, at a given instant, in opposite directionsthrough said secondary gaps but in generally the same radial directionthrough said primary gap.

10. An alternating current electric circuit interrupter of thevacuum-type comprising:

(a) an evacuated envelope,

(b) means for establishing a magnetic field comprising two sub-fields,each of generally toroidal shape, the two generally toroidal sub-fieldssurrounding a common axis and being axially displaced from each otheralong said axis,

(c) said two sub-fields being developed in bucking relationship to eachother so as to extend, at a given instant, in opposite directions alongsaid axis and in generally the same radial direction in the region wherethe two sub-fields are adjacent each other,

((1) a primary arcing gap inside said envelope, radially spaced fromsaid axis and located in the region where said two sub-fields areadjacent each other, said sub-fields extending transversely of saidprimary (e) an annular secondary arcing gap in said envelope locatedradially outward of said primary gap and displaced therefrom along saidaxis so that one of said sub-fields extends longitudinally of saidsecony s p,

(f) means for establishing an arc across said primary gap with themagnetic field in the immediate region of the are extending generallynormal-to said are,

(g) and means for transferring at least a portion of said are to saidsecondary gap with the portion of said are in said secondary gapextending generally parallel to the magnetic field in said secondary gapin the region of the are, 4

(h) said magnetic field in said secondary gap being high enough tosubstantially reduce the arc voltage of high current arcs present insaid secondary gap as compared to the are voltage normally developed byand are of equal current burning across said secondary gap without saidmagnetic field.

11. An alternating current electric circuit interrupter of thevacuum-type comprising:

(d) a primary arcing gap inside said envelope, radially spaced from saidaxis and located in the region where said two sub-fields are adjacenteach other, said sub-fields extending transversely of said pri- (e) apair of annular secondary arcing gaps inside said envelope, each locatedradially outward of said primary arcing gap and in a difierent one ofsaid subfields,

(f) said annular secondary arcing gaps being located in positionsaxially spaced from said primary gap where the respective sub-fieldsextend generally parallel to said axis and across said secondary gapgenerally longitudinally thereof,

(g) means for establishing an arc across said primary gap with saidsub-fields extending generally normal to said arc,

(h) means located between said primary and secondary gaps for dividingsaid are into a pair of series-related arcs,

(i) and means for respectively transferring said seriesrelated arcs tosaid secondary gaps with each secondary are extending generally parallelto the sub-field extending across its associated secondary gap,

(j) said magnetic field in said secondary gaps being high enough tosubstantially reduce the are voltage of high current arcs present insaid secondary gaps as compared to the arc voltage normally developed byarcs of equal current burning across said secondary gaps without saidmagnetic field.

References Cited UNITED STATES PATENTS 2,027,836 1/1936 Rankin.

2,090,519 8/ 1937 Rankin.

2,949,520 8/ 1960 Schneider.

2,976,382 3/1961 Lee 200-144 3,014,107 12/1961 Cobine et a1 200-1443,082,307 3/ 1963 Greenwood et al. 200144 3,185,797 5/1965 Porter 200144 3,185,799 5/ 1965 Greenwood et al. 200-144 3,283,103 11/1966Greenwood et al. 200 -l44 FOREIGN PATENTS 571,959 1/1958 Italy.

ROBERT S. MACON, Primary Examiner.

